Martyrs' Day (Spanish: Día de los Mártires) is a Panamanian day of national mourning which commemorates the January 9, 1964 anti-American riots over sovereignty of the Panama Canal Zone. The riot started after a Panamanian flag was torn and students were killed during a conflict with Canal Zone Police officers and Canal Zone residents. It is also known as the Flag Incident or Flag Protests.

U.S. Army units became involved in suppressing the violence after Canal Zone police were overwhelmed, and after three days of fighting, about 22 Panamanians and four U.S. soldiers were killed. The incident is considered to be a significant factor in the U.S. decision to transfer control of the Canal Zone to Panama through the 1977 Torrijos–Carter Treaties.